Metabolism is a defining feature of all living organisms without exception. Isolated metabolic reactions in vitro are not living things but surely living reactions. Comment.
Metabolism is the sum of all synthesing (anabolic) and breaking down (catabolic) reactions. These are highly specific and enzymatically controlled reactions, which take place inside all the individual cells of unicellular or multicellular organisms.
These are infact the basis of life. These reactions help organism to grow, reproduce, maintain their steady state and respond to stimuli. It can be understood by taking example of digestion.
All organisms need nutrition in the form of food, which is digested by metabolic reactions either intracellularly or extracellularly depending upon the type of organisms. So, all reactions which help the organisms to breakdown food molecules and then assimilate them for their growth and reproduction are metabolic reactions.
Few reactions may be performed outside the cells, under controlled conditions, Chemical reactions usually involve specific set of conditions to take place. All biological reactions are highly specific, selective and are enzyme catalysed.